1. Field of the Invention
This invention relates to a projection type display apparatus such as a liquid crystal projector.
2. Related Background Art
There is a projector carrying an auto focusing apparatus thereon. This auto focusing apparatus is designed such that an operator operates (pushes) a focusing switch, whereby a focusing operation is performed and the focus of an image projected onto a screen is adjusted. Also, as auto focusing (AF) techniques, there are known active methods of measuring the propagation time of an ultrasonic signal to thereby find a distance and effect AF (Japanese Patent Application Laid-Open No. 4-338707), and of projecting infrared light and receiving the reflected light thereof to thereby find a distance by the principle of trigonometrical distance measurement and effect AF, and a passive method of reading the contrast of brightness on a screen by a pair of light receiving line sensors, and obtaining the correlative values of respective pixel outputs to thereby find a distance and effect AF, etc.
Also, in the projector, so-called trapezoidal distortion in which distortion occurs onto an image is caused when the direction of a normal to the surface of a screen and the direction of the optical axis of projected light deviate from each other. When for example, as shown in FIG. 9 of the accompanying drawings, a projector main body 2 is installed with an elevation from horizontal with respect to a screen 1, an image projected onto the screen 1 becomes distorted as indicated by a projected image 3. As a proposition for automatically effecting the correction of such trapezoidal distortion, there is a projector described in Japanese Patent Application Laid-Open No. 8-9309. In this reference, the distances among at least three points on the projector and the screen are measured to thereby detect the inclination of the surface of the screen, and such image data as will offset the distortion of a displayed image is projected to thereby make automatic trapezoidal distortion correction possible. Also, in Japanese Patent Application Laid-Open No. 2001-186538, there is proposed a display apparatus in which the distortion of an image on the surface of a screen is calculated from the projection angle of projected light and the installation angle of a projector main body to thereby automatically correct trapezoidal distortion.
Here, the automatic focus adjusting function realized by the various focus detecting methods as described above is executed by operating a focusing switch, and the automatic trapezoidal distortion correcting function is also executed by operating a correction switch. Operating the operation switch of each function leads to the problem that a user's operation is cumbersome and the operability of a displaying apparatus is spoiled. Also, when the focus adjusting function and the trapezoidal distortion correcting function are being performed, there is the problem that an image of which the focus is blurred (which is out of focus) or an image of which the shape is distorted is projected and an image of low quality is displayed for a long time until a good projected image is displayed.